1. Field of the Invention
The present invention relates to locking mechanisms for doors that are locked and unlocked electrically.
2. Description of Related Art
Motorized locking mechanisms are used in applications that require a lock to be operated electrically. Although there are many such applications, one illustrative use is in the outside handle trim for an exit device operated by a keypad. Outside trim of this type is installed on the exterior side of an exit door of a commercial building where the exit door will also be used by authorized personnel to enter the building. The trim piece includes a handle having a spindle that turns a hub. The spindle extends through the exit door and into the exit device mounted on the inner side of the door.
Motorized locks used in this application typically have a motor that drives a locking slide into and out of locking engagement with a hub on a spindle attached to the handle. Turning the handle rotates the hub and opens the door. Preventing the hub from turning locks the trim and prevents access. The hub generally includes a locking notch in its perimeter that receives the locking slide to prevent rotation of the hub and the handle. The motor drives the locking slide into and out of interfering engagement with the locking notch in the hub to lock and unlock the door.
In a keypad-controlled device, the user enters a numeric code into the keypad to open the door. Entry of the correct code energizes the motor and electrically retracts the locking slide from the hub for a short period of time—the “access period”. During the access period, the handle may be rotated and the door opened. After the access period, the locking slide is driven back into the hub to relock the exit door and prevent unauthorized entry.
A particular problem with motorized locking mechanisms relates to the forces that can be applied from the hub to the locking mechanism through the locking slide. Particularly when the handle is a lever handle, a very high level of torque can be applied to the hub. This high level of torque can apply a damaging level of force to the internal components of the locking mechanism through the locking slide. The locking slide will attempt to turn with the turning hub in response to forces applied to the handle. This turning motion is not in the direction required to open the door, and is resisted by a counteracting force applied to the locking slide by the mounting of the locking slide. Thus, door security is not compromised.
However, the locking slide may cock or move slightly in undesired ways, particularly under high load levels when the lock mechanism is worn. This undesired motion can drive the motor or other parts of the locking mechanism in undesired and potentially damaging directions and/or apply a damaging level of force to the motorized system for moving the locking slide.
Another problem with motorized designs of this type is that the locking slide may be temporarily prevented from moving to or from the locked position. If the handle is still in the rotated position when the access period expires, the locking slide cannot re-engage the locking notch in the hub. Alternatively, if a turning force is applied to the handle before the access period begins, friction between the hub and the locking slide may prevent the locking slide from being retracted.
It is particularly important that the motorized lock ensure that door is correctly relocked after the access period. Although inconvenient, a user can simply operate the lock again if he has prevented the door from unlocking by prematurely applying a rotational force to the handle. However, if the user has prevented the mechanism from relocking, by keeping the handle rotated beyond the access period, the door will remain unlocked if the motorized lock is incapable of relocking automatically after the handle is released.
One method of achieving automatic relock is to monitor the location of the locking slide and re-energize the motor if the slide has not moved. This method is relatively expensive to implement due to the cost of the sensors and additional electronics required. A related difficulty is that the motor system must be properly designed so that it does not damage itself or any other part of the lock if the motor is energized while the locking slide is prevented from moving.
It is known to provide for automatic relock by using a spring, but in some applications it is preferred for the locking slide to move vertically. The use of a spring for automatic relock of a motor-driven, vertically moving, locking slide has been problematical. The motor and drive mechanism must lift the weight of the locking slide through the spring and prevent it from returning during the access period.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a motorized locking mechanism that prevents damaging forces from being transferred to the locking mechanism from the device being locked.
It is another object of the present invention to provide a motorized locking mechanism suitable for vertical use.
It is a further object of the present invention to provide a motorized locking mechanism that is modular for easy installation during manufacturing and rapid replacement in the field.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.